The investigational aims of this protocol are: 1) to ascertain and characterize previously unidentified inborn errors; 2) to delineate distinct clinical or genetic variants of known inborn errors; 3) to develop innovative rational therapeutic approaches in inborn errors; 4) to identify and characterize the clinical and chemical consequences of established and novel treatment protocols in inborn errors. Underlying these objectives is the notion that patients with acute metabolic encephalopathy, or more chronic or slowly progressive encephalopathies, can be recognized by distinct patterns of clinical presentations, and can be categorized for systematic study on the basis of a carefully chosen battery of clinical chemistries. We hypothesize that such baseline clinical evaluations and categorizations will enable the identification of patients with potential new disorders, and serve to identify patients with established inborn errors in whom distinct clinical, biochemical or molecular variants can be characterized.